With the development of the communication technology advances, the home-used communication devices are gradually replaced by the mobile communication devices, such as smart phone and pad computer, and smart appliances can comprise the communication apparatuses installed therein. The mobile communication devices and smart appliances perform wireless communications for an objective of data transmissions, and thus the era of internet-of-thing (IoT) comes in people life.
The wireless communication is implemented by a transceiver to transmit and receive the wireless signal on air. The transceiver ally has a frequency synthesizer for switching the carrier frequencies. For the demand of high communication quality, a stable and accurate local oscillating (LO) signal is imperatively required since this can make the wireless signal be accurately transmitted to a wireless receiver. Thus, the low phase noise voltage controlled oscillator (VCO) is an important electrical component in the transceiver.
Now, a standard of 5th generation (5G) mobile communication is developing, and compared with the previous generation mobile communication, 5G mobile communication provides a higher network capacity, a higher data transmission rate, a more robust communication ability and a lower wireless transmission delay. Additionally, the standard of 5G mobile communication specifies a radio frequency (RF) from 38.6 GHz through 40 GHz.
Referring to FIG. 1, FIG. 1 is a block diagram of a conventional transceiver used in 5G mobile communication. The conventional transceiver 1 comprises a modulator 11, sub-harmonic mixers 12, 17, a power amplifier (PA) 13, a transmitting/receiving-switch (TR-SW) 14, an antenna 15, a low noise amplifier (LNA) 16, a demodulator 18 and a phase locked loop (PLL) 19. The sub-harmonic mixer 12 is connected to the modulator 11, the PLL 19 and the PA 13. The TR-SW 14 is connected to the PA 13, the LNA 16 and the antenna 15. The sub-harmonic mixer 17 is connected to the demodulator 18, the PLL 19 and the LNA 16.
The modulator 11 receives and modulates a first data signal Din to generate a first intermediate frequency (IF) signal of about 3.5 GHz. The PLL 19 provides a LO signal to the sub-harmonic mixers 12 and 17. The sub-harmonic mixer 12 mixes the first IF signal and the LO signal to generate a first RF signal to the PA 13. The PA 13 receives and amplifies the first RF signal, and the TR-SW is switched to the PA 13, such that antenna 15 can radiate the first amplified RF signal to air.
The antenna 15 can receive a second RF signal from air, and the TR-SW is switched to the LNA 16, such that the LNA 16 can amplify the second RF signal. The sub-harmonic mixer 17 mixes the second amplified RF signal and the LO signal to generate a second IF signal of about 3.5 GHz. The demodulator 18 receives and demodulates the second IF signal to generate a second data signal Dout.
In the standard of 5G mobile communication, the RF is specified from 38.6 GHz through 40 GHz, and the RF can be expressed as RF=2LO+IF. Thus, the LO should be designed in the range of 17.55 GHz through 18.25 GHz. To prevent process variation or other effecting factor, the range of the LO can be extended from 17.2 GHz through 18.6 GHz, so as to meet the standard of 5G mobile communication.
In addition to that the PLL is used to generate the LO signal, a conventional QVCO can be also used to generate LO signals of quadrature phases, but the conventional QVCO has a coupling network is connected to output ends thereof, such that the output load is increased, and the maximum operating frequency is decreased. Furthermore, the current passive coupling network may induce phase offsets at different frequencies due to an ultrawide operating band.